Increased Expression of α6 Integrin in Endothelial Cells Unveils a Proangiogenic Role for Basement Membrane

Abstract

The integrin α6 subunit is part of the α6β1 and α6β4 integrin complexes, which are known to be receptors for laminins and to mediate several biological activities such as embryogenesis, organogenesis, and invasion of carcinoma cells. However, the precise role of α6 integrin in angiogenesis has not yet been addressed. We observed that both vascular endothelial growth factor-A and fibroblast growth factor-2 strongly upregulate α6 integrin in human endothelial cells. Moreover, α6 integrin was positively modulated in angiogenic vessels in pancreatic neuroendocrine carcinoma. In this transgenic mouse model of spontaneous tumorigenesis, α6 integrin expression increased in the angiogenic stage, while being expressed at low levels in normal and hyperplastic tissue. We studied the functional role of α6 integrin during angiogenesis by lentivirus-mediated gene silencing and blocking antibody. Cell migration and morphogenesis on basement membrane extracts, a laminin-rich matrix, was reduced in endothelial cells expressing low levels of α6 integrin. However, we did not observe any differences in collagen matrices. Similar results were obtained in the aortic ring angiogenesis assay. α6 integrin was required for vessel sprouting on basement membrane gels but not on collagen gels, as shown by stably silencing this integrin in the murine aorta. Finally, a neutralizing anti-α6 integrin antibody inhibited in vivo angiogenesis in chicken chorioallantoic membrane and transgenic tumor mouse model. In summary, we showed that the α6 integrin participated in vascular endothelial growth factor-A and fibroblast growth factor-2-driven angiogenesis in vitro and in vivo, suggesting that it might be an attractive target for therapeutic approaches in angiogenesis-dependent diseases such as tumor growth. Cancer Res; 70(14); 5759-69. ©2010 AACR.

Vascular Normalization as a Therapeutic Strategy for Malignant and Nonmalignant Disease

“…Preclinical studies have used a number of approaches including (1) specific VEGF blockade with agents that interfere with VEGF binding to its receptors (including antihuman VEGF antibodies such as A4.6.1 and bevacizumab), antimurine VEGF antibodies, and the "VEGF-Trap" aflibercept; (2) inhibition of VEGFR2 function (using anti-VEGFR2 antibodies such as DC101 or receptor tyrosine kinase inhibitors [TKIs] which inhibit the kinase domain of VEGFRs). In addition, elegant preclinical work examining the role of Yuan et al 1996;Tong et al 2004;Dickson et al 2007b;Taguchi et al 2008;Falcon et al 2009;Juan et al 2009;Kamoun et al 2009;Chae et al 2010;Koh et al 2010;Primo et al 2010. b Jain et al 1998;Izumi et al 2002;Delmas et al 2003;Qayum et al 2009. d Inai et al 2004;Tong et al 2004;Nakahara et al 2006;Dickson et al 2007b;Dings et al 2007;Fischer et al 2007;Zhou et al 2008;Falcon et al 2009;Juan et al 2009;Kamoun et al 2009;Ohta et al 2009;Zhou and Gallo 2009;Chae et al 2010;Primo et al 2010.…”

“…In addition, elegant preclinical work examining the role of Yuan et al 1996;Tong et al 2004;Dickson et al 2007b;Taguchi et al 2008;Falcon et al 2009;Juan et al 2009;Kamoun et al 2009;Chae et al 2010;Koh et al 2010;Primo et al 2010. b Jain et al 1998;Izumi et al 2002;Delmas et al 2003;Qayum et al 2009. d Inai et al 2004;Tong et al 2004;Nakahara et al 2006;Dickson et al 2007b;Dings et al 2007;Fischer et al 2007;Zhou et al 2008;Falcon et al 2009;Juan et al 2009;Kamoun et al 2009;Ohta et al 2009;Zhou and Gallo 2009;Chae et al 2010;Primo et al 2010. Lee et al 2000;Winkler et al 2004;Dings et al 2007;Fischer et al 2007;Eichhorn et al 2008;Batra et al 2009;Skuli et al 2009;McGee et al 2010.…”

“…These include the EC-specific integrins (Friedlander et al 1995;Kurozumi et al 2007;Skuli et al 2009;Desgrosellier and Cheresh 2010;Primo et al 2010), semaphorins (Bielenberg et al 2006;Maione et al 2009), members of the nitric oxide synthase family (Kashiwagi et al 2005(Kashiwagi et al , 2008Yu et al 2005), TGF-b (Liu et al, submitted for publication), and interferon-b (Dickson et al 2007a,c;Taylor et al 2008). In keeping with the notion that it is the balance between pro-and antiangiogenic stimuli that moderates the equilibrium between normal and abnormal vessels, modulation of the activity of these molecules is able to normalize tumor vessels structurally and/or functionally in a variety of tumor models preclinically.…”

Modeling human tumor angiogenesis in a three-dimensional culture system

“…mAR assays were performed as previously described. 9 In brief, thoracic aortas were removed from 8-to 12-week-old wild-type C57/BL6 mice (Charles River) and fibroadipose tissue was dissected away. Aortas were sectioned into 1-mm-long aortic rings and incubated for 2 days in serum-free medium with antibiotics.…”

“…Adaptations of this assay allow direct monitoring of the angiogenic process and the study of endothelial tip cell dynamics. [8][9][10][11] However, rat and mAR models display certain disadvantages: a high age-and strain-dependent variability of assays, 12 as well as variations owing to the region of the explanted aorta 13 ; autonomous angiogenic outgrowth, limiting studies on proangiogenic factors 14 ; the necessity to sacrifice animals; and the failure to detect species-specific antiangiogenic compounds in preclinical screening assays. 15 In this study, we developed an ex vivo three-dimensional (3D) assay of sprouting angiogenesis with arterial explants from human umbilical cords.…”